Bush wouldn't have gone as far with the "Reaganism" agenda - he would have been more of a Nixon/Ford conservative.
Unclear if he would have won in 1984 or not - someone like Gary Hart could have beat him, but the improving economy in fall 1984 would have helped any incumbent.
The problems underlying the decay of the USSR existed by March 1981 (including the Afghanistan war) - I think at that point the decline of the USSR was entirely inevitable, though it's possible that it may have been longer or different.
I mean, would Hart get caught with a woman?